It explains that PTC is current limiting and CID is for overvoltage/overheating. And it also explains why we fuse packs instead of just relying on PTC and CID.

There is no safe way to test for this, you have to expect thermal runaway and prepare for it. Even if the cell survives, discharge it completely and recycle it as it may have become compromised during testing.

To test for PTC, short the cell. I used a typical 4 cell holder and soldered a wire from positive to negative and left room for a clamp meter to clamp on. I used an infrared thermometer to watch the cell temperature. I did this for 2 generic cells and will do it for a lot more soon. If the cell has PTC, once you insert the cell, you will see the Amps on the clamp meter go from something like 30+amps down to whatever the PTC protection was designed to limit to. In my case, a fully charged 4.2V cell dropped from 35Amps to 1.8Amps and stayed there for 10 minutes before I ended the test. The temperature of the cell rose to about 155*F/70*C and also stayed around that temperature for the duration of the test. If the cell did not have PTC, it would have entered thermal runaway.

To test for CID, overcharge the cell. I haven't done this yet, but I plan on hooking up a 12V 1Amp plug directly to an 18650 (probably through the 4 cell holder for convenience and monitoring). I believe 12V is the industry standard as I've seen it referenced in a few data sheets. For the few CIDs I reset (dumb idea, but I was a noob at the time) all were around 4.20V upon reset, so likely the CID tripped due to overcharge. I do believe they can trip due to heat as well, so if you have a scrap toaster oven, try heating up a cell to 100*C while charging it or something like that?